Photographic developing machines



Sept. 4, 1956 E; L. CROSS 2,761,364

PHOTOGRAPHIC DEVELOPING MACHINES Filed June 20, 1951 INVENTOR EDWARD LESLIE CRoss United States Patent PHOTOGRAPHIC DEVELOPING MACHINES Edward Leslie Cross, London, England, assignor to Ozalrd Company Limited, London, England, a British company Application June 20, 1951, Serial No. 232,545 Claims priority, application Great Britain June 26, 1950 2 Claims. (CI. 95-89) This'invention relates to methods and apparatus for developing photographic sensitised material and of the type (hereinafter referred to as the type described) in which material, after a printing operation involving exposure to light, is subjected to humid alkaline vapour contained within a chamber (hereinafter referred to as. the developing chamber) and generated from an aqueous solution of ammonia or other gaseous alkaline developing agent.

Methods of the type described are commonly used for the development of sensitised paper or like material in sheet form carrying a light-sensitive diazo compound together with a coupling component, the two being prevented from coupling by the presence of an acidic. substance, the inhibiting action of which is neutralised by the ammonia or other developing gas, whereupon the formation of an azo-dyestulf takes place. In developing apparatus of the type described it is usual to feed the developing solution into a tray or the like situatedin a chamber or tank having an upper wall of, perforated material over the outer surface of which the sensitised material is traversed, the developing solution being vaporised by electric or other heating elements located within the tank.

In the operation of methods and apparatus of the type described certain practical diificulties arise in connection with the handling of the developing solution and the generation and maintenance of correctly proportioned development atmosphere. With ammonia solutions of a concentration (e. g. specific gravity 0.908) such as usually employed, there is a tendency for water vapour to condense upon the perforated plate. or equivalent surface over which the material isv passed for development and thereby to cause staining of the material. Such condensation may be avoided-or the risk of it minimised-by the application of excess heat (i. e. in excess of that necessary to effect evaporation of the developing solution) to the developing chamber but the resulting high temperature may have an adverse effect on the light sensitive material. If, for the purpose of avoiding these ill effects, highly concentrated solutions of ammonia (having a specific gravity of say 0.880) are used, other drawbacks are encountered. Such solutions are diflicult to handle. In the containers in which the solution is supplied a considerable gas pressure may be created when the ambient temperature is high, e. g. in a warm room and particularly in the summer, and as a result transference of the solution from its container to the reservoir of the apparatus is attended by the escape of extremely noxious fumes. Again, with such highly concentrated solutions it is diflicult to maintain a regular flow from a drip feed apparatus which is the usual method of regulating the ammonia supply.

An object of the present invention is to overcome or at least minimise the above difficulties.

The invention provides a method of the type described for developing photographic sensitised material, which is characterised by effecting, external to the developing chamber, (a) the evaporation of a supply of a developing solution and (b) the condensing out of the resulting mixture of water vapour and gaseous developing agent of a portion of its water content; the thus partially de humidified mixture being then conveyed to the developing chamber to act as the development atmosphere.

With the above method an ammonia, solution of normal concentration (e. g. specific gravity 0.908) may be employed, thus avoiding the disadvantages--already mentioned-attendant upon the handling and feeding of more highly concentrated solutions. At the same time, by the step of dehumidifying the evaporated solution, the gas concentration in the development atmosphere is increased and the risk of condensation within. the developing chamber is thereby reduced without entailing the use of a chamber temperature which might adversely affect the sensitised material.

The invention includes apparatus for carrying out the above method, comprising in combination a developing,

chamber having an upper perforated wall over which the sensitised material may be traversed and having means for heating the chamber, an evaporating chamber with an associated heater, means for supplying developing solution at a controlled rate to the evaporating chamber, a vapour condenser (preferably controllable as to the extent of its condensing action) and a vapour flow conduit communicating between the evaporating and developing chambers viathe condenser.

An example of the invention will now be. described with reference to the accompanying drawing which is a diagrammatic illustration of the apparatus.

In this example the apparatus comprises a developing chamber of known type (see British specification No. 495,392) the upper wall 2 of which is perforated and surmounted by the lower lap of an endless belt conveyor 3 of non-permeable rubber. The belt 3 is supported on end rollers 4, at least one of which is driven. The arrangement is such that exposed prints may be fed, from one end of the developing chamber into the region between the perforated wall 2 and the lower advancing lap of the belt 3 and so traversed over the perforated wall to the other end of the chamber, during which time the sensitised surface of each print (which is arranged to face the perforated wall) will be exposed, through the perforations, to the development atmosphere.

According to this invention, generation of the development atmosphere is effected, outside the developing chamher, by the following means. An evaporating chamber 5 is fitted with an internal tray 6 located above an electrical heating element 7 and arranged to receive, by drip feed, a supply of ammonia solution from a reservoir 8 by way of a conduit 9. A needle valve 10 or equivalent device is provided for controlling the rate of supply of the solution. A vapour flow conduit 11 communicates between the top of the evaporating chamber 5 and the inlet to a condenser 12, whereof the outlet communicates by a vapour flow conduit 13 with the interior of the developing chamber. The condenser may be of any convenient type employing any desired coolant. It may for example take the form of a thin walled tube surrounded by a jacket through which air may be circulated at a controlled rate (and, if desired, under variable temperature conditions) so that the amount of water vapour condensed may be varied at will. For the removal of the water condensed out of the humid ammonia vapour, the condenser 12 is furnished with a drain 14, fitted with any convenient form of vapour seal. The vapour flow conduit 13 leading to the interior of the developing chamber, may be coupled to one end of a longitudinal distributing tube 15 provided with a longitudinal slot (not shown) forming the vapour outlet from the tube. The developing chamber is provided with a heating element 16 extended along the chamber below the distributing tube.

In operation the reservoir 8 is filled with aqueous ammonia solution, the heating elements 7 and 16 in the evaporating and developing chambers are switched on and a controlled flow of ammonia solution is admitted to the tray 6 of the evaporating chamber. The rate of feed of the solution and the temperature within the evaporating chamber are so controlled as to ensure continuous and substantially complete evaporation of the ammonia supplied. The humid ammoniacal vapour passes upwardly through the conduit 11 to the condenser 12 where part of the water vapour returns to the liquid phase while the partially dehumidified ammoniacal vapour passes out of the top of the condenser, through the cinduit 13 and into the developing chamber. Although the condensate reabsorbs some ammonia gas, the quantity is relatively small.

The apparatus provides for various adjustments being made to suit different operating conditions, and in particular different rates of feed of prints over the perforated wall of the developing chamber. For example the quantitative rate of feed of the solution to the evaporating chamber may be decreased to correspond with a reduction in the rate at which the prints are fed and vice-versa. Again, to suit different conditions, the ratio of the volume of liquid drained off from the condenser to the volume of ammonia solution fed to the evaporating chamber may be varied by an appropriate variation in the rate of circulation and/or temperature of the coolant in the condenser. In every case the internal temperatures in the evaporating and developing chambers are maintained above 100 C. while the temperature of the condenser walls is maintained below 100 C.

The following is an example of a practical test with one form of the apparatus:

The apparatus was brought to an operational condition and sheets of diazotype material were passed over the developing chamber at a rate of approximately 30 ft. per minute. The ammonia supply in the form of a solution of 0.908 s. g. was controlled at 25 ccs. per minute. The internal temperature of the evaporating chamber was maintained at 105 C., and the internal temperature of the developing chamber at 115 C. The temperatures of the vapour entering and leaving the condenser were 90 C. and 69 C. respectively. For every 100 ccs. of solution added, approximately 48 ccs. of dilute ammonia solution were obtained as condensate.

The above test was continued for an extended period and no sign of condensation on the developed prints appeared.

I claim:

1. Apparatus for developing a photographic sensitized material with partially dehumidified ammoniacal vapor obtained from solutions of ammonia having a specific gravity of about 0.908 comprising, in combination, a storage chamber for aqueous ammonia solution, a development chamber having an upper perforated wall over which the sensitized material may be passed, and having means remote from the perforated plate, for heating the chamber to a temperature of about 115 C., a vaporizing chamber located external to said development chamber, a supply conduit for feeding aqueous ammonia solution from said storage chamber to said vaporizing chamber, heating means connected to said vaporizing chamber for heating the same to about 105 C. and arranged to effect substantially complete vaporization of the aqueous ammonia solution supplied to said vaporizing chamber, a vapor condenser located external to said development chamber adapted to receive the vapor generated in said vaporizing chamber at substantially atmospheric pressure and condense out therefrom a portion of the water vapor content, and flow conduit arranged to supply the partially dehumidified ammoniacal vapor from said vapor condenser, to said development chamber.

2. Apparatus for developing a photographic sensitized material with partially dehumidified ammoniacal vapor obtained from solutions of ammonia having a specific gravity of about 0.908 comprising in combination a storage chamber for aqueous ammonia solution, a development chamber having an upper perforated wall over which the sensitized material may be passed, and having means remote from said plate, for heating the chamber to about 115 C., a vaporizing chamber located external to said development chamber, a supply conduit for feeding aqueous ammonia solution from said storage chamber to said vaporizing chamber, a control device for controlling the rate of feed of the aqueous ammonia solution by said conduit, heating means connected to said vaporizing chamber for heating the same to about 105 C. and arranged to effect substantially complete vaporization of the aqueous ammonia solution supplied to said vaporizing chamber, a vapor condenser located external to said development chamber adapted to receive the vapor generated in said vaporizing chamber at substantially atmospheric pressure and condense out therefrom a portion of the water vapor content, means for controlling the condensing effect of the vapor condenser and a flow conduit arranged to supply the partially dehumidified ammoniacal vapor from said vapor condenser to said development chamber.

References Cited the file of this patent UNITED STATES PATENTS 

